Wood-chip preparation for digesters from unbarked logs



May 6, 1952 A. B. DUNWODY WOOD-CHIP PREPARATION FOR DIGESTERS FROM UNBARKED LOGS 2 Sl-IEETS-Si-IEET 1 Filed Nov. 2, 1948 CUT LOG CHIFPER lTi SEPARATOR y 6, 1952 A. B. DUNWODY 2,596,015

WOOD-CHIP PREPARATION FOR DIGESTERS FROM UNBARKED LOGS Filed Nov. 2, 1948 2 SHEETS-SI-IEET a [HI EHZ'UP A rchibald B. Dzzizwaqy Z75 Hill/5 Patented May 6, 1952 VVOOD-CHIP PREPARATION FOR DIGES- TERS FROM UNBARKED LOGS Archibald B. Dunwody, Evanston, Ill.

Application November 2, 1948, Serial No. 57,947

1 Claim. 1

The present invention relates to a wood chipping process and more particularly to a process for the preparation of wood chips free of foreign material and having uniform chemical and physical characteristics.

Prior to the present invention, the preparation of wood chips for paper manufacturing from cut logs has involved the removal of bark from the logs as by peeling, chipping the logs, screening the chips to remove very coarse material and fines and recycling the coarse material through a chip breaker and the screening step. Following screening, the accepted chips are placed in temporary storage for subsequent introduction into the digester of the pulping process. The process, generally as above outlined, has been employed in the paper manufacturing industry for many years, even though the chips thus prepared are undesirable in several particulars for the manufacture of fine, uniform paper. For example, this process produces chips which include knots, ingrown bark, decayed wood and incidental dirt. The density of accepted chips varies in accordance with the particular type or batch of wood and even within each log from which the chips are prepared, and the moisture content of the chips varies from batch to batch.

The separate log peeling operation requires the use of expensive, specialized apparatus and requires skilled, hand labor. Due to the inclusion of incidental dirt, elaborate control devices and methods have been developed for separating dirt from the pulp prepared from dirty chips, as by screening, centrifugal separation, and by settling in fluid mass. The presence of knots, bark and decayed wood has a deleterious effect upon the quality of the paper produced from the chips, since the cooking process must be carried out under conditions sufficiently severe to digest knots, even though overcooking the desirable e clear chips lowers the pulp quality andstrength.

Also, the varying pitch content, density and other chemical and physical characteristics of the chips have made impossible the uniform treatment and refining of pulp prepared from trolled within narrow limits. Not only is the quality of chips enhanced with a consequent upgrading of the type of paper obtained from any given variety or species of wood, but also the process is simplified by the elimination of the log peeling operation. In accordance with the present invention, it is not necessary to remove the bark from the cut logs prior to the chipping operation, since the separation of bark from acceptable chips is accomplished following the chipping operation. The process herein described also provides means for controlling the quality of chips from any desirable source by effecting a separation of the chips in accordance with their apparent bulk density into a plurality of fractions. That fraction having the heaviest apparent density contains a concentration of knots or chips containing a large amount of pitch. The second heaviest fraction contains the most desirable, clear dense wood chips suitable for the manufacture of the highest grades of premium or top quality paper. Less dense fractions contain chips suitable for the preparation of kraft or similar papers while the lightest fractions contain pulpy or decayed wood chips, dirt, bark and other foreign material.

The process of the present invention includes the step of chipping unpeeled cut logs into chips of desirable size. Following the chipping operation, the chips are preferably introduced into an air float separator or other apparatus to effect the separation of the chips in accordance with their apparent bulk density. Following the separation of the chips, those chips particularly desirable for the manufacture of top quality paper are further refined in accordance with practices conventional in the art, the less desirable chips are used to manufacture lower grades of paper, and the dirt and fines fraction, that fraction having the lowest apparent density, may be employed as fuel. In some cases, it is desirable to dry the chips directly following the chipping operation in order that chips having a uniform moisture content may be more readily separated and refined. Also, if desired, the chips may be rough-screened prior to their separation into desirable and undesirable fractions as hereinbefore described, the screening serving merely to regulate the size of chip subsequently introduced into the separator.

it is, therefore, an important object of the present invention to provide an improved process for the production of wood chips having uniform physical and chemical characteristics, the chips being free from foreign material and desirable for use in the manufacture of paper.

It is another important object of the present invention to provide a wood chipping process which eliminates the separate peeling or debarkingoperation of the prior art while yielding chips having desirable physical and chemical properties.

It is a still further important object of the present invention to provide a wood chipping process wherein wood chips are separated in accordance with their apparent bulk density into fractions particularly desirable for the various grades of paper now being commercially m duced.

It is a yet further important object of the present invention to provide a wood chipping process quality paper, a second fraction suitable for the manufacture of lower grades of paper and additional fractionscontaining knots, dirt, bark and other foreign materials normally present in wood ch s- Other and further important objects of this invention will be apparent from the disclosures in the specification and accompanying drawings.

On the drawings:

Figure l is a flow diagram illustratin the processof the present invention;

Figure 2 is an elevational View, with parts broken away, of a wood chipper suitable for use in the process of the present invention;

Figure 3 is a perspective view of air flotation apparatus suitable for use in the process of the present invention; and

Figure 4 is a diagrammatic representation illus trati'n'g. the separation of wood chips into fr'actions in accordance with the principles of the present invention.

As shown on the drawings:

Figure 1 illustrates, in diagrammatic form, the various steps of the wood chipping process of the present invention, while the apparatus illustrated in Figures 2 and 3 may be suitably employed for carrying out the necessary steps of. the process. It should be realized that the apparatus; illus: trated in Figures 2 and 3 is merely exemplary of suitable apparatus for carrying out the process herein described.

In accordance with my process, a cut log, sawed or cut to the desired length, is formed into relatively small chips by apparatus 'such'as that illustrated in Figure 2. In Figure 2, reference numeral it refers generally to a cut log having bark still present on its exterior surface. Log Hlis formed into suitably sized chips by. means of a conventional chipper. ll comprising a'shaft l2 journaledin supports 13 and I4 mountedv on a suitable standard it. The shaft l2: carries a crowned fly wheel l5 receiving a belt ll lapped thereabout for transmitting rotational movement to the fly wheel it from a suitable source of power (not shown). The shaft l2 may thus be rotated bymeans offly wheel l6 which also serves as a power transmitting pulley.

A'cutti-ng disk 58 provided with a plurality of radially extending sharpened blades i9 is dispose-d on the shaft l2 for rotation therewith.

Chips cut from log is may pass freely through the openings 28 in disk ii! for a purpose to; be hereinafter described. The log H3 is guided in a chute 2! inclined to the axis of the shaft I2 s0 that the log 10 is gravity fed by the chute into contact with the sharpened forward edges'of blades l9. The moving blades is upon rotation of the shaft 12 come in contact with that edge of the log I0 extending in close proximity to the cutting disk IS. The chips produced by the cutting of the end of the log by the blades it pass through the apertures or slots 2B of the cutting disk 'Iil'and fall into a pit 22 defined by the base l5 and a vertically extending baffle plate 23. The chips may be removed from the pit 22 in any desired manner, either continuously or intermittently. The apparatus ll thus functions as described. to p'rovi'demeans for chipping the log it into a plurality of finely divided chips suitable for introduction into the subsequent refining steps of the paper manufacturing process.

"Following the chipping operation above described, the chips may suitably be dried, as in a conventional drum type drier, so that the moisture; content ofchips preparedfrom different log batches may be uniform. However, it should be understood that under some conditions, as when a- 'relatively large batch of logs of a single species or from a single source is being employed, this drying is not necessary. This drying step, by the more or. less complete removal of Water, reduces the majority of, chips from a single log or batch of logs to a definite proportional bulk density so thatjthe'efficie ncy of the later steps of the method isfi'ncre'asedjas hereinafter more fully explained. and, thisdryingstepprovides a ready means for controlling the moisture content of the digester iritd' the chips are subsequently charged. In'ge e'rarr ipre ferto dry the chips prior to the scjreening step, although desirable results may bedbtaii'ied' withoutthe necessity of this step.

Following the drying operation, the chips may, if desired, beTscreened to size the chips to give a"urfii'forlh. product. This screening operation is carried out merely to size the chips, inasmuch as theseparationofthe chips into various fractions havmgaienn chemical and physical characteristicsis. preferably carried out during the later perfsrmedse araung step.

The 'emps'airecu'yi from the chipper, or from the subsequent. drying and screening operations, are next. intrnduce'd'into apparatus for separatfrom foreign material and other gjre'dierits by. means of their apparei'itbi lli' density." I have found that apparatus "Iiilthe. apparatus illustrated in Figure 3, reference, numeral 25frefe'r's generally to a separating apparatus comprising a horizontally oscillating bed 'Z'G a'iidT a' stationary base 27. The bed 26 is car ed by the base'21. so that the upper bed surface 28 is inclined to. the horizontal with its out let. edgegfi, being lowered with reference to the inlefdge3.0"andwith the foremost portion iii of the. bedZbeingfe levated with reference to lower ed isza offtheinlet chute 32 positioned at the rearm ost portion of the bed 28. The base 21 carries a suitable source'of power, such as an electricmotor'iis, adapted for driving means contained inthe. base 21 for horizontally oscillating the bed-28. The base l! also carries an air inlet conduit 34 connected at one end to air filtering means 35, and; at its other end to air impelling means, such as a. fan (not shown), driven by jii'floati separator shown in Figure employed for this separation themotor. 33. and;.adapted to direct a blast of air with a surface covering 36 of closely woven wire or fabric. The wire or fabric coating 36 is supported by a plurality of parallel ribs Bl extending longitudinally of the bed 28, the covering depending between the ribs 3'! to form a rifiled surface Suitable results have been obtained by the employment of beds 28 made of 16 mesh wire of 0.041 inch diameter, the bed having a ratio of open to closed areas of 11.6 to 100. The bed may be inclined so that the angle of inclination from inlet side 30 to outlet side 29 varies from 15 to 3, and from the lower edge 32a of inlet chute 32 to the opposite edge 3| varies from 2 to 5. For example, side inclinations of 2 and end inclinations of 3 have been employed. The amount of air blown through bed 28 may vary from 2100 to 4000 cubic feet per minute, with a preferred air flow of about 3400 cubic feet per minute. The riflles 31 may vary from about 0.375 to 1.5 inches in height at the lower edge 32a of inlet chute 32 of the bed 28. These heights diminish to zero at the edge opposite the inlet chute 32 so that the obstruction becomes .less as the particle density increases.

It should be understood that the dimensions and conditions above outlined may be varied as desired to accommodate the apparatus of Figure 3 to the separation of any desired type of wood-chips Without departing from the principles of my invention. For example, air how will vary directly with the density and quantity of chips introduced into the bed 28, while the deck slope of inclination willalso vary with the chip density, size, etc.

In the operation of the separating apparatus illustrated in Figure 3, chips are introduced through the inlet chute 32 onto the riiiled surface 28. The chips are moved by the horizontal oscillating movement of the bed across the surface of the bed as in a conventional oscillating conveyor. However, the air flowing upwardly through the porous surface 36 tends to support the lighter chip particles above the surface. The lighter particles, floating in the buoyant air stream, touch the oscillating bed surface less frequently than the heavier particles so that less longitudinal movement is imparted to the lighter particles by the oscillating movement of the bed. Accordingly, the heavier particles move across the surface of the bed in a direction indicated generally by the dotted directional arrow 40 of Figure 4. The next lighter particles follow a path illustrated generally by directional arrow 4| with the progressively lighter particles following the paths indicated at 42 and 43 respectively. The rifiled surface, provided by the foraminous covering 36 overlying the ribs 3'1, tends to prevent the heavier particles from moving toward the lowered outlet edge 29 under the influence of gravity. However the lighter particles coming into less frequent contact with the oscillating bed will be capable of movement across the ribs 31 due to the buoyant effect of the upward air flow through the bed. Accordingly, the chips will be discharged along the discharge edge 29 at points longitudinally spaced in accordance with their apparent bulk density. After passing over the outlet edge 29, the fractions are free to fall vertically under the influence of gravity into their respective discharge hoppers 44 from which the fractions may be collected by any suitable means. It will thus be seen that the particles may be readily separated in accordance with their apparent bulk density by means of the apparatus illustrated in Figures 3 and 4:-

TABLE I Physical evaluation of chips Quantity Based on Original Chips Per Cent Fraction Number Remarks Very high percent of chips containing knots. Clean, sound, knot-free. Contained small and decayed chips, small amount: of bark and dirt. Sawdust size, much bark and dirt.

Table I clearly illustrates the excellent separation of chips containing knots, small and decayed chips, bark and dirt from the total chip output of the chipper by means of air flotation apparatus.

In the following data, fraction 4 of Table I, containing saw dust, bark and dirt, was discarded and the first three fractions were tested for comparison with a control fraction prepared by con-- ventional means from a peeled spruce log by conventional chipping apparatus and subsequent screening in the usual chip screens.

Table II illustrates the difference in density between the fractions of Table I:

TABLE II Density of chips 45 ngn/nsitly s. on. t i ractiou Number Green Volume Control 20. 7 1 22. 5 2 20. 5 3 l8. 7

Extract Based on Oven Dry Weight of Wood Fraction Number Per cent The data in Table III clearly show the low pitch. content of fraction 2, which factor adds materially to the quality of paper pulp obtained from the chips constituting this fraction.

Chips of fractions 1, 2 and 3 and of the con- 111101 fraction were submitted to the conventional sulfite pulping operation and subsequent testing bymethods well known in the art with the results'set forth in Table IV:

TABLE IV .S'u-Zfite pulping evaluation of chips Bleachability Screened Screening Pulp Fraction Number As Bleach Pulp Yield Yield Strength Powder Per Cent Per Cent Factor Per Cent This table clearly shows the improved bleachability, pulp yield and pulp strength factor obtained from fraction 2 over that obtained by the use of the conventional chips of the control fraction. Also, the screening yield, indicating nona'cceptable sized chips, is considerably lower in fraction 2.

The pulp obtained as described in connection with Table IV was evaluated by means of an alcohol extraction and ether extraction to determine the amount of pitch contained in the pulp. Theresul-ts are presented in Table V:

7 TABLE V Pulp evaluation Alcohol Ether T0011 motion Number Soluble Soluble t Extract Extract O l. 06 0. 78 .1. 84 l. 40 0. 97 2. 37 0. 83 0. 64 l. 47 1. 28 0. 84' 2. l2

TABLE VI Dirt count on hand sheets Fraction Number From the results above set forth, it is evident that pulp of improved quality possessing enhanced physical and chemical characteristics is readily obtained by practicing the method of the present invention. Fraction 2, that fraction containing clean, sound, knot-free chips and having a mean apparent bulk density of approximately 20.5 lbs/cubic foot, is the preferred fraction for the manufacture of top quality paper. This fraction constitutesiabout 80% of the total chip flow introduced into the airflotation separation process. This fraction, being relatively free of pitch, dirt, and other undesirable foreign ingredients, when employed for the manufacture of paper pulp results in the upgrading of paper quality obtained from any given variety of wood. The fractions 1 and 3 containing those chips having a high percentage of knots and also those chips containing decayed matter, some dirt and bark, are useful for the preparation of kraft papers, standard papers, and other less desirable end products;

Those skilled in the art will, of course, understand that the complete process of chipping, drying, screening, and separating may be employed to prepare desirable chips for subsequent refining. Each step prepares the wood being processed for the subsequent steps of the method, and in the preferred method, the drying step, by insuring constant moisture content in the chips subjected to later separation and digestion, makes possible the accurate process control of these later steps, while preliminary screening improves operation of the process by permitting more accurate separation on the basis of bulk density and the better chemical circulation and heat transfer during refining. Alternatively, of course, either or both of the drying and screening steps may be eliminated while still obtaining improved results over the prior art procedures.

Uniform cooking and refining of acceptable chips is insured upon the subjection of uniform material to the refining process and the necessity of screening to remove dirt and other foreign matter from the pulp is eliminated. Further, varieties of wood formerly believed to be unsuitable for use in the preparation of quality papers may now be employed by utilizing the process of the present invention to prepare chips having desired chemical and physical characteristics.

The paper produced from chips prepared by my process is not only improved in quality but also the speed of operation'is increased since recycling, overcooking to digest knots, and other expedients heretofore necessary need not be employed in utilizing chips prepared by my process. The process herein described eliminates the formerly necessary time-consuming and expensive peeling or debarking operation. The screening of the chips may be eliminated with a consequent increase in production and decrease in apparatus expense and time. Many other-advantages which will be readily evident to those-skilled in the art may be obtained by the process of the present invention.

It will, of course, be understood that Various details of the process may be varied through a wide range without departing from the principles of this invention, and it is, therefore, not the purpose to limit the patent granted hereonotherwise than necessitated by the scope of the appended claim.

I claim as my invention:

A process for the preparation of wood chips from unbarked logs, which comprises chipping into relatively small chips a log having its bark still on, drying the resulting chips from many such logs of substantially the same species of wood to a substantially uniform moisture content, screening the dried chips to approximate uniformity :of size, passing .saiddried and screened chips into the high side of an inclined, rifiied and air permeable surface, oscillating said surface while blowing a gaseous stream upwardly therethrough, all under such conditions as to separate said chipsinto fractions on the basis of apparent bulk density, collecting the following fractions separately as the chips are discharged from the lower side of said surface: a .fraction of substantially uniform intermediate bulk density containing clean, barkand knot-free chips suitable for manufacture into high grade paper; another fraction of relatively higher bulk density containing knots, another fraction of relatively lower bulk density containing decayed Wood, some bark and dirt; and still another fraction containing much bark and dirt, and temporarily storing said first-mentioned fraction for subsequently digesting into pulp, whereby the greater uniformity in the size and quality of the chips in said fraction and their lower, more uniform moisture content make for better and more accurate control in the digesting step.

ARCHIBALD B. DUNWODY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 556,111 Talbot Mar. 10, 1896 Number Name Date 557,718 Talbot et a1. Apr. 7, 1896 675,833 Jones June 4, 1901 931,120 Hunicke Aug. 17, 1909 1,057,151 Howard Mar. 25, 1913 1,579,993 Andre Apr. 6, 1926 1,632,520 Sutton June 14, 1927 1,710,521 Sutton Apr. 23, 1929 1,982,601 Sutton Nov. 27, 1934 2,225,459 Palmrose Dec. 17, 1940 2,236,806 Sutton Apr. 1, 1941 2,264,421 Ward Dec. 2, 1941 2,315,372 Kressman Mar. 30, 1943 2,356,775 Mechlin Aug. 29, 1944 2,361,601 Carter Oct. 31, 1944 2,446,551 Pauley Aug. 10, 1948 OTHER REFERENCES Chemical Engineers Handbook, by Perry, 2nd edition, 1941, McGraw-Hill Book C0,, New York and London, Dry Tables, page 1727. 

